diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 5fcfa40..2b5e933 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -138,6 +138,7 @@ python_install_on_site(pyhpp/pinocchio utils.py)
 python_install_on_site(pyhpp/manipulation constraint_graph_factory.py)
 python_install_on_site(pyhpp/core static_stability_constraint_factory.py)
 python_install_on_site(pyhpp/manipulation security_margins.py)
+python_install_on_site(pyhpp/manipulation spline.py)
 
 add_python_library(
   pyhpp/pinocchio
diff --git a/src/pyhpp/manipulation/spline.py b/src/pyhpp/manipulation/spline.py
new file mode 100644
index 0000000..15f1a48
--- /dev/null
+++ b/src/pyhpp/manipulation/spline.py
@@ -0,0 +1,67 @@
+"""Spline smoothing of paths carrying manipulation graph constraints."""
+
+from pyhpp.core import Straight
+from pyhpp.core.path import Vector
+from pyhpp.manipulation import SplineGradientBased_bezier3
+
+
+class ManipulationSpline(SplineGradientBased_bezier3):
+    """Smooth transitions, then join splines within each manipulation state.
+
+    The result contains one PathVector per consecutive group of transitions
+    with the same containing state. These groups can be timed independently
+    to preserve stops at state changes.
+
+    ``singleSplineTransitions`` selects transitions to fit from their endpoints
+    using their existing constraints, for example constrained insertion motions.
+    Other transitions retain their interpolation intervals as the initial spline
+    pieces. Input paths must be geometric paths with correct transition labels.
+    """
+
+    def __init__(self, problem, graph):
+        super().__init__(problem)
+        self.graph = graph
+        self.straight = Straight(problem)
+        self.singleSplineTransitions = ()
+        self.costOrder = 2
+        self.maxIterations(100)
+
+    def optimize(self, path):
+        """Return smoothed state groups with their graph constraints preserved."""
+        flat = Vector(path.outputSize(), path.outputDerivativeSize())
+        path.flatten(flat)
+        groups = []
+        previous = None
+        cursor = 0.0
+        for rank in range(flat.numberPaths()):
+            leaf = flat.pathAtRank(rank)
+            start, cursor = cursor, cursor + leaf.length()
+            if cursor - start <= 1e-9:
+                continue
+            name = self.graph.transitionAtParam(path, (start + cursor) / 2).name()
+            if name != previous:
+                groups.append(Vector(path.outputSize(), path.outputDerivativeSize()))
+                previous = name
+            groups[-1].appendPath(leaf)
+
+        states = []
+        previous = None
+        for group in groups:
+            if group.length() < 1e-6:
+                raise ValueError("Path transition is too short for spline timing")
+            transition = self.graph.transitionAtParam(group, group.length() / 2)
+            if transition.name() in self.singleSplineTransitions:
+                self.straight.constraints(group.pathAtRank(0).constraints())
+                insertion = self.straight(group.initial(), group.end())
+                group = Vector(path.outputSize(), path.outputDerivativeSize())
+                group.appendPath(insertion)
+            state = self.graph.getContainingNode(transition)
+            if state != previous:
+                states.append(Vector(path.outputSize(), path.outputDerivativeSize()))
+                previous = state
+            states[-1].concatenate(super().optimize(group))
+
+        result = Vector(path.outputSize(), path.outputDerivativeSize())
+        for group in states:
+            result.appendPath(super().optimize(group))
+        return result